1. Field of the Invention
The present invention relates to the field of display screens. More specifically, an embodiment of the present invention relates to the field of flat panel displays for portable electronic devices, such as personal digital assistants (PDAs), cell phones, pagers, digital watches etc.
2. Background of the Invention
Flat panel displays are commonly used in portable computer devices to display images and characters. The viewing area of some display panels is generally illuminated with at least one light source. The light source may be positioned behind or in front of the display matrix layer. The light from the light source may be distributed uniformly across the display panel. The efficiency of light distribution, uniformity of the distribution, intensity of the illumination and color of the light illuminating the display panel has always been a subject of development and improvement.
The efficiency of light distribution may be function of several factors including maximizing the use of the light source available and improving the light source used. Maximization of any resource can substantially be achieved by prevention of waste. In providing light to a display screen, light pipes are used to transfer the light from a light source across the display screen. Maximized use of the light source can be achieved using a light pipe that increases the amount of reflected light that illuminates the display matrix.
Flat panel display thickness is always a concern regarding portable electronic devices. Each layer of a flat panel display screen adds cost and thickness to the display subassembly. The display component of many portable electronic devices typically contributes a significant percentage of the overall thickness of the device. Therefore, it would be desirable to reduce the thickness of a flat panel display subassembly to thereby reduce the overall thickness of the portable electronic device.
Another factor of concern for maximizing illumination efficiency of a display screen is the color of the light used for illumination. For instance, a white color light is an appealing color for the users of portable devices under many environments. Commonly, white light may be achieved by using blue LEDs which illuminate an epoxy secured phosphor layer. These conventional displays have a very limited lifetime, maybe a few thousand hours due to heat related phosphor degradation. Consumers may not tolerate such a short lifetime for portable devices.
Thus a need exists for a portable computer system having a uniformly bright display screen which is efficiently illuminated. Furthermore, a need exists for a portable computer with a display screen properly illuminated to prevent undue stress on the user""s eyes. Additionally, a need exists for such a flat panel display screen having a white color source with extended operating life.
Embodiments of the present invention provide a portable electronic device, e.g., a computer system, pager, cell phone, etc., with a thin, uniformly bright display screen, which is efficiently illuminated. Furthermore, one embodiment of the present invention provides a portable computer with a display screen properly illuminated to prevent undue stress on the user""s eyes. Additionally, another embodiment of the present invention provides a white color light source with an improved operating life over conventional systems.
An efficient technique for illuminating a display screen in a portable computer is disclosed. One embodiment discloses vapor deposition of a highly reflective material around the non-viewing areas of a light pipe for providing light to a display matrix area of the display screen. The brightness enhancement film may be made of silicon oxide (SiO2) or titanium oxide (TiO2), or combination of metal oxides for instance. The vapor deposited reflector may be used in front lighting and backlighting embodiments. Another embodiment further discloses deposition of reflective material on the surface of microstructures (of the light pipe) to enhance light reflection and to prevent light escape. Another embodiment of the present invention discloses a display technique using vapor deposition or coating of a phosphor layer on a light pipe for producing long lasting white light.
With respect to the back lighting embodiments, the reflective material may be vapor deposited on the back surface, and some of the sides of the light pipe. With respect to the front lighting embodiments, reflective material may be vapor deposited on the sides of the light pipe.
More specifically, an embodiment of the present invention discloses a flat panel display assembly comprising a flat panel display layer for generating an image using discrete elements; and a planar light pipe disposed to receive light from a light source and for back-illuminating the flat panel display layer from a rear position, the planar light pipe comprising a reflective material deposited on its bottom surface, the reflective material deposited on the planar light pipe using a chemical vapor deposition process. An embodiment include the above and wherein the light pipe has thereon a vapor-deposition or coating deposited phosphor layer.
A second embodiment discloses a flat panel display assembly comprising a flat panel display layer for generating an image using discrete elements; a planar light pipe disposed to receive light from a light source and for illuminating the flat panel display layer from a front position, the planar light pipe comprising a reflective material deposited on the edges of the light pipe thereon using a chemical vapor deposition process.